Acoustic wave device with transverse mode suppression

ABSTRACT

Aspects of this disclosure relate to an acoustic wave device with transverse mode suppression. The acoustic wave device can include a piezoelectric layer, an interdigital transducer electrode, a temperature compensation layer, and a multi-layer mass loading strip. The mass loading strip has a density that is higher than a density of the temperature compensation layer. The mass loading strip can overlap edge portions of fingers of the interdigital transducer electrode. The mass loading strip can include a first layer for adhesion and a second layer for mass loading. The mass loading strip can suppress a transverse mode.

CROSS REFERENCE TO PRIORITY APPLICATION

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/785,919, filed Dec. 28, 2018 and titled“ACOUSTIC WAVE RESONATOR WITH TRANSVERSE MODE SUPPRESSION,” thedisclosure of which is hereby incorporated by reference in its entiretyherein.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices withtransverse mode suppression.

Description of Related Technology

Piezoelectric microelectromechanical systems (MEMS) resonators can beused in radio frequency systems. Piezoelectric MEMS resonators canprocess electrical signals using mechanically vibrating structures.Example piezoelectric MEMS resonators include surface acoustic (SAW)resonators and temperature compensated surface acoustic wave (TC-SAW)resonators.

Acoustic wave filters can include TC-SAW resonators. Acoustic wavefilters can filter radio frequency signals in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. Multiple acoustic wavefilters can be arranged as a multiplexer, such as a duplexer.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

In one aspect an acoustic wave device is disclosed. The acoustic wavedevice can include a piezoelectric layer, an interdigital transducerelectrode disposed over the piezoelectric layer, and a temperaturecompensation layer disposed over the interdigital transducer electrode.The interdigital transducer electrode include a bus bar and a pluralityof fingers that extend from the bus bar. The fingers each includes anedge portion and a body portion. The acoustic wave device can alsoinclude a mass loading strip that overlaps the edge portions of thefingers. The mass loading strip has a density that is higher than adensity of the temperature compensation layer. The mass loading stripincludes a first layer and a second layer. A portion of the temperaturecompensation layer is positioned between the mass loading strip and thepiezoelectric layer. The mass loading strip is arranged to suppress atransverse mode.

In one embodiment, the first layer of the mass loading strip ispositioned between the second layer of the mass loading strip and theinterdigital transducer electrode. The first layer of the mass loadingstrip can have higher adhesion to the temperature compensation layerthan the second layer of the mass loading strip. The second layer of themass loading strip can have a higher mass than the first layer of themass loading strip. The second layer of the mass loading strip is aconductive strip.

In one embodiment, the mass loading strip is positioned between thesecond layer of the mass loading strip and the interdigital transducerelectrode. The first layer of the mass loading strip can includetitanium. The second layer of the mass loading strip can includemolybdenum. The interdigital transducer electrode can includemolybdenum. The second layer of the mass loading strip can include atleast one of tungsten, gold, silver, ruthenium, copper, platinum, oriridium.

In one embodiment, the first layer of the mass loading strip ispositioned between the second layer of the mass loading strip and theinterdigital transducer electrode. The second layer of the mass loadingstrip can have a mass sufficient to suppress the transverse mode.

In one embodiment, the mass loading strip is embedded in the temperaturecompensation layer.

In one embodiment, the acoustic wave resonator is configured to generatea surface acoustic wave.

In one embodiment, the temperature compensation layer is a silicondioxide layer.

In one embodiment, the temperature compensation layer has a thicknessfrom a lower surface to an upper surface opposite the lower surface. Themass loading strip can be spaced apart from the lower surface by adistance that is within 20% to 80% of the thickness of the temperaturecompensation layer.

In one embodiment, the acoustic wave resonator further includes asilicon nitride layer over the temperature compensation layer.

In one embodiment, the temperature compensation layer has a thicknessfrom a lower surface to an upper surface opposite the lower surface. Themass loading strip can be spaced apart from the lower surface by adistance that is within 40% to 60% of the thickness of the temperaturecompensation layer.

In one embodiment, the second layer has a higher density than a densityof the interdigital transducer electrode.

In one embodiment, the mass loading strip includes a third layer. Thethird layer of the mass loading strip can include titanium.

In one aspect, a surface acoustic wave resonator is disclosed. Thesurface acoustic wave resonator can include a piezoelectric layer, aninterdigital transducer electrode disposed over the piezoelectric layer,and a temperature compensation layer disposed over the interdigitaltransducer electrode. The interdigital transducer electrode includes abus bar and fingers extending from the bus bar. The fingers eachincludes an edge portion and a body portion. The surface acoustic waveresonator can also include a mass loading strip that overlaps the edgeportions of the fingers. The mass loading strip includes a first layerand a second layer. The mass loading strip has a density that is higherthan a density of the temperature compensation layer. The first layer ispositioned between the second layer and the interdigital transducerelectrode. The first layer having higher adhesion with the temperaturecompensation layer than the second layer. The second layer has a highermass than the first layer. A portion of the temperature compensationlayer is positioned between the mass loading strip and the piezoelectriclayer. The surface acoustic wave resonator is configured to generate asurface acoustic wave. The mass loading strip is arranged to suppress atransverse mode.

In one embodiment, the first layer of the mass loading strip includestitanium. The second layer of the mass loading strip can includemolybdenum. The second layer of the mass loading strip can include atleast one of tungsten, gold, silver, ruthenium, copper, platinum, oriridium.

In one embodiment, the second layer has a mass density that is greaterthan or equal to a mass density of the interdigital transducerelectrode.

In one embodiment, the mass loading strip is embedded in the temperaturecompensation layer.

In one embodiment, the temperature compensation layer is a silicondioxide layer. The surface acoustic wave resonator can further include asilicon nitride layer disposed over the temperature compensation layer.

In one aspect, an acoustic wave filter is disclosed. The acoustic wavefilter can include an acoustic wave resonator including a piezoelectriclayer, an interdigital transducer electrode disposed over thepiezoelectric layer, a temperature compensation layer disposed over theinterdigital transducer electrode, and a multi-layer mass loading stripthat overlaps edge portions of fingers of the interdigital transducerelectrode. The multi-layer mass loading strip has a higher density thanthe temperature compensation layer. The acoustic wave filter can alsoinclude a plurality of other acoustic wave resonators that coupled tothe acoustic wave resonator. The acoustic wave resonator and the otheracoustic wave resonators are together arranged to filter a radiofrequency signal.

In one embodiment, the multi-layer mass loading strip is a multi-layermass loading strip.

In one embodiment, front end module can include the acoustic wavefilter, additional circuitry, and a package that encloses the surfaceacoustic wave filter and the additional circuitry.

In one embodiment, the multi-layer mass loading strip includes a firstlayer and a second layer. The first layer can be positioned closer tothe interdigital transducer electrode than the second layer. The firstlayer can have a higher adhesion to the temperature compensation layerthan the second layer.

In one aspect, front end module including an acoustic wave filter,additional circuitry, and a package enclosing the surface acoustic wavefilter and the additional circuitry is disclosed. The acoustic wavefilter can include an acoustic wave resonator including a piezoelectriclayer, an interdigital transducer electrode disposed over thepiezoelectric layer, a temperature compensation layer disposed over theinterdigital transducer electrode, and a multi-layer mass loading stripthat overlaps edge portions of fingers of the interdigital transducerelectrode. The multi-layer mass loading strip has a higher density thanthe temperature compensation layer. The acoustic wave filter can alsoinclude a plurality of other acoustic wave resonators that coupled tothe acoustic wave resonator. The acoustic wave resonator and the otheracoustic wave resonators are together arranged to filter a radiofrequency signal.

In one embodiment, the additional circuitry includes a multi-throw radiofrequency switch.

In one embodiment, the additional circuitry includes a power amplifier.

In one embodiment, a wireless communication device can include anantenna and an acoustic wave filter. The acoustic wave filter caninclude an acoustic wave resonator including a piezoelectric layer, aninterdigital transducer electrode disposed over the piezoelectric layer,a temperature compensation layer disposed over the interdigitaltransducer electrode, and a multi-layer mass loading strip that overlapsedge portions of fingers of the interdigital transducer electrode. Themulti-layer mass loading strip has a higher density than the temperaturecompensation layer. The acoustic wave filter can also include aplurality of other acoustic wave resonators that coupled to the acousticwave resonator. The acoustic wave resonator and the other acoustic waveresonators are together arranged to filter a radio frequency signal.

In one aspect, a method of manufacturing an acoustic wave resonator isdisclosed. The method can include providing an acoustic wave resonatorwith a temperature compensation layer disposed over an interdigitaltransducer electrode. The interdigital transducer electrode includesfingers that extend from a bus bar. The fingers each including an edgeportion and a body portion. The method can also include forming a firstlayer of a mass loading strip that overlaps with the edge portions ofthe fingers of the interdigital transducer electrode. Material of thetemperature compensation layer is positioned between the first layer ofthe mass loading strip and the interdigital transducer electrode. Themethod further includes depositing a second layer of the mass loadingstrip disposed over the first layer of the mass loading strip. The firstlayer of the mass loading strip has a higher adhesion than the secondlayer of the mass loading strip. The second layer of the mass loadingstrip has a higher mass than the first layer of the mass loading strip.

In one embodiment, the first layer includes titanium. The second layercan include molybdenum.

In one embodiment, the method comprises forming temperature compensationmaterial over the second layer of the mass loading strip.

In one embodiment, the temperature compensation layer is a silicondioxide layer.

In one embodiment, the first layer of the mass loading strip is formedwithin 20% to 80% of the thickness of the temperature compensation layerfrom a piezoelectric layer of the acoustic wave resonator.

In one embodiment, the method further include depositing a siliconnitride layer over the temperature compensation layer. The first layerof the mass loading strip can be positioned within 40% to 60% of thethickness of the temperature compensation layer from a piezoelectriclayer of the acoustic wave resonator.

In one aspect, a method of filtering a radio frequency signal isdisclosed. The method can include receiving a radio frequency signal atan input port of an acoustic wave filter that includes an acoustic waveresonator. The acoustic wave resonator includes a multi-layer massloading strip overlapping edge portions of fingers of an interdigitaltransducer electrode. The method can also include filtering the radiofrequency signal with the acoustic wave filter. The filtering includessuppressing a transverse mode using the multi-layer mass loading stripof the acoustic wave resonator.

In one embodiment, a first layer of the multi-layer mass loading striphas a higher adhesion to a temperature compensation layer than a secondlayer of the multi-layer mass loading strip. At least a portion of thetemperature compensation layer can be positioned between the multi-layermass loading strip and the interdigital transducer electrode. The secondlayer of the multi-layer mass loading strip can have a higher mass thanthe first layer of the multi-layer mass loading strip.

In one embodiment, the multi-layer mass loading strip includes atitanium layer.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the innovations have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment. Thus, theinnovations may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1A illustrates a cross section of a surface acoustic wave (SAW)resonator according to an embodiment.

FIG. 1B illustrates a top view of the SAW resonator of FIG. 1A.

FIG. 1C illustrates a side view of the metal strip of the SAW resonatorof FIG. 1A.

FIG. 1D illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 1E illustrates a top view of the SAW resonator of FIG. 1D.

FIG. 1F illustrates a side view of the metal strip of the SAW resonatorof FIG. 1D.

FIG. 1G illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 1H illustrates a cross section of a SAW resonator according to anembodiment.

FIG. 1I illustrates a top view of the SAW resonator of FIG. 1H.

FIG. 2 illustrates a cross section of a surface acoustic wave resonatoraccording to an embodiment.

FIG. 3 illustrates a cross section of a surface acoustic wave resonatorwith a delaminated metal strip.

FIG. 4A is a graph showing a measurement of an admittance of theresonator of FIG. 3.

FIG. 4B is a graph showing a measurement of an admittance of theresonator of FIG. 3 without a metal strip being delaminated.

FIG. 4C is a graph showing a measurement of an admittance of theresonator of FIG. 1A.

FIG. 5 illustrates a cross section of a portion of a surface acousticwave resonator according to an embodiment.

FIG. 6 is a graph showing simulated velocities of a surface acousticwave in surface acoustic wave resonators.

FIG. 7A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 7B illustrates a top view of the SAW resonator of FIG. 7A.

FIG. 8A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 8B illustrates a top view of the SAW resonator of FIG. 8A.

FIG. 9A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 9B illustrates a top view of the SAW resonator of FIG. 9A.

FIG. 10A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 10B illustrates a top view of the SAW resonator of FIG. 10A.

FIG. 11A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 11B illustrates a top view of the SAW resonator of FIG. 11A.

FIG. 12A illustrates a cross section of a SAW resonator according toanother embodiment.

FIG. 12B illustrates a top view of the SAW resonator of FIG. 12A.

FIG. 13A illustrates a cross section of a Lamb wave device according toan embodiment.

FIG. 13B illustrates a cross section of a Lamb wave device according toanother embodiment.

FIG. 14A is a schematic diagram of a transmit filter that includessurface acoustic wave resonators according to an embodiment.

FIG. 14B is a schematic diagram of a receive filter that includessurface acoustic wave resonators according to an embodiment.

FIG. 15 is a schematic diagram of a radio frequency module that includesa surface acoustic wave component according to an embodiment.

FIG. 16 is a schematic diagram of a radio frequency module that includesa surface acoustic wave component according to an embodiment.

FIG. 17A is a schematic block diagram of a wireless communication devicethat includes a filter in accordance with one or more embodiments.

FIG. 17B is a schematic block diagram of another wireless communicationdevice that includes a filter in accordance with one or moreembodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Acoustic wave filters can filter radio frequency (RF) signals in avariety of applications, such as in an RF front end of a mobile phone.An acoustic wave filter can be implemented with surface acoustic wave(SAW) devices. SAW devices include SAW resonators, SAW delay lines, andmulti-mode SAW (MMS) filters (e.g., double mode SAW (DMS) filters).

In general, high quality factor (Q), large effective electromechanicalcoupling coefficient (k² _(eff)), high frequency ability, and spuriousfree can be significant aspects for micro resonators to enable low-lossfilters, stable oscillators, and sensitive sensors. SAW resonators canhave a relatively strong transverse mode in and/or near a pass band. Thepresence of the relatively strong transverse modes can hinder theaccuracy and/or stability of oscillators and sensors, as well as hurtthe performance of acoustic filters by creating relatively severepassband ripples and possibly limiting the rejection.

Therefore, transverse mode suppression method is significant for SAWresonators. A technical solution for suppressing transverse modes is tocreate a border region with a different velocity from a central part ofthe active region according to the mode dispersion characteristic. Thiscan be referred to as a “piston mode.” A piston mode can be obtained tocancel out the transverse wave vector in a lateral direction withoutsignificantly degrading the k² or Q. By including a relatively smallborder region with a slow velocity on the edge of the acoustic apertureof a SAW resonator, a propagating mode can have a zero (or approximatelyzero) transverse wave vector in the active aperture. This may beachieved by providing a multi-layer conductive strip on edges of aninterdigital transducer (IDT) electrode active regions of the SAWresonator. The transverse wave vector can be real in the border regionand imaginary on a gap region. A piston mode SAW resonator can have evenorder modes that have a multiple of full wave lengths in the activeregion, which should not significantly couple to electrical domain.

When a relatively high density metal strip is used to achieve a pistonmode in a temperature compensated surface acoustic wave (TC-SAW)resonator, the high density metal strip can be buried in a temperaturecompensation layer. The high density metal strip may have a relativelyweak adhesion with the temperature compensation layer. A relatively weakadhesion strength between the high density metal strip and thetemperature compensation layer can lead to delamination of the highdensity metal strip from the temperature compensation layer. When thedelamination occurs, the transverse mode may not be sufficientlysuppressed.

A metal strip can include molybdenum to obtain mass loading for pistonmode operation. However, molybdenum is not particularly adhesive and canexperience delamination. Titanium has good adhesion. However, titaniummay not have sufficient mass loading desired for piston mode operation.A stacked molybdenum/titanium strip is provided to obtain adherence andmass loading for piston mode operation in an acoustic wave resonator.Titanium can provide desirable crystal orientation for an overlyinglayer, such as a molybdenum layer over the titanium.

Aspects of this disclosure relate to SAW resonators (e.g., TC-SAWresonators) that include a metal strip that includes a high densitymetal layer and an adhesion layer. The metal strip can be buried in atemperature compensation layer, such as a silicon dioxide layer. Theadhesion layer can provide an adhesion strength that can mitigate and/orprevent delamination of the metal strip from the temperaturecompensation layer. The high density layer can provide mass loading forpiston mode operation. Accordingly, a SAW device with a multi-layer massloading strip is disclosed.

Although embodiments may be discussed with reference to multi-layermetal strips or multi-layer conductive strips, any suitable principlesand advantages disclosed herein can be applied to a multi-layer massloading strip that includes one or more non-conductive layers. Moreover,although embodiments may be discussed with reference to SAW resonators,the principles and advantages discussed herein can be applied to anysuitable SAW device and/or any other suitable acoustic wave device.Embodiments will now be discussed with reference to drawings. Anysuitable combination of features of the embodiments disclosed herein canbe implemented together with each other.

FIG. 1A illustrates a cross section of a surface acoustic wave (SAW)resonator 1 according to an embodiment. The SAW resonator 1 can bereferred to as a temperature compensated SAW (TCSAW) resonator. The SAWresonator 1 includes a piezoelectric layer 10, an IDT electrode 12 overthe piezoelectric layer 10, a temperature compensation layer 14 over theIDT electrode 12, and a metal strip 16 buried in the temperaturecompensation layer 14. The illustrated metal strip 16 includes a highdensity metal strip layer 18 and an adhesion layer 20. Accordingly, themetal strip 16 is a multi-layer conductive strip. A multi-layer metalstrip can include three or more layers in some other embodiments. Themulti-layer metal strip 16 performs a mass loading function.Accordingly, the multi-layer metal strip 16 is an example of amulti-layer mass loading strip. The IDT electrode 12 includes fingers 22and bus bars 24.

The piezoelectric layer 10 can be a piezoelectric substrate. Thepiezoelectric layer 10 can include any suitable piezoelectric layer,such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer.A thickness of the piezoelectric layer 10 can be selected based on awavelength λ or L of a surface acoustic wave generated by the surfaceacoustic wave resonator 1. The IDT electrode 12 has a pitch that setsthe wavelength λ or L of the surface acoustic wave resonator 1. Thepiezoelectric layer 10 can be sufficiently thick to avoid significantfrequency variation. In certain applications, the piezoelectric layer 10can have a thickness in a range from about 30 micrometers to 600micrometers. For example, the piezoelectric layer 10 can have athickness in a range from about 100 micrometers to 200 micrometers insome applications.

The temperature compensation layer 14 can include any suitable material.For example, the temperature compensation layer 14 can be a silicondioxide (SiO₂) layer. The temperature compensation layer 14 can be alayer of any other suitable material having a positive temperaturecoefficient of frequency. For instance, the temperature compensationlayer 14 can be a tellurium dioxide (TeO₂) layer or a siliconoxyfluoride (SiOF) layer in certain applications. A temperaturecompensation layer can include any suitable combination of SiO₂, TeO₂,and/or SiOF.

The temperature compensation layer 14 can bring the temperaturecoefficient of frequency (TCF) of the SAW resonator 1 closer to zerorelative to a similar SAW resonator without the temperature compensationlayer 14. In certain applications, the temperature compensation layer 14can improve the electromechanical coupling coefficient k² of the SAWresonator 1 relative to a similar SAW resonator without the temperaturecompensation layer 14. This advantage of the temperature compensationlayer 14 can be more pronounced when the SAW resonator 1 includes an LNlayer as the piezoelectric layer 10. The temperature compensation layer14 has a thickness t1 measured from a lower surface 14 a to an uppersurface 14 b opposite the lower surface 16 a. In some embodiments, thethickness t1 of the temperature compensation layer 14 can be in a rangefrom 0.1 L to 0.5 L. For example, when the wavelength L is 4 μm, thethickness t1 of the temperature compensation layer 14 can be 1200 nm.

The IDT electrode 12 can include any suitable material. For example, theIDT electrode can include molybdenum (Mo) in certain embodiments. TheIDT electrode 12 can include a plurality of metal layers, for example,as shown in FIG. 2. The IDT electrode 12 may include one or more othermetals, such as copper (Cu), Magnesium (Mg), tungsten (W), titanium(Ti), platinum (Pt), gold (Au), silver (Ag), iridium (Ir), ruthenium(Ru), etc. The IDT electrode 12 may include alloys, such as AlMgCu,AlCu, etc. The IDT electrode 12 has a thickness t2. In some embodiments,the thickness t2 of the IDT electrode 12 can be about 0.05 L. Forexample, when the wavelength L is 4 μm, the thickness t2 of the Mo layer18 can be 200 nm.

FIG. 1B illustrates a top view of the SAW resonator 1 of FIG. 1A. Thetemperature compensation layer 14 is not illustrated to show the IDTelectrode 12 and the metal strip 16. The dashed lines between FIGS. 1Aand 1B show relative positions of the illustrated components. Theillustrated SAW resonator 1 of FIGS. 1A and 1B includes two bus bars 24and three fingers 22 extending from each of the bus bars 24. Each finger22 has a proximate end 22 a that is in contact with a bus bar 24 and adistal end 22 b opposite the proximate end 22 a. A body portion 22 c ofthe finger 22 extends between the proximate end 22 a and the distal end22 b. A portion near the distal end 22 b can be referred as an edgeportion. The edge portion (the distal end 22 b) can be adjacent toand/or near the edge of the finger 22. In some embodiments, the edgeportion can include the edge of the finger 22. In some otherembodiments, the edge portion can offset from the edge of the finger 22by about 0.1λ or less. With the edge portion offset from the edge of thefinger 22 by 0.1λ, there can be no significant performance degradation.

FIG. 1C illustrates a side view of the metal strip 16 of FIG. 1A. Themetal strip 16 includes the high density layer 18 and the adhesion layer20. As illustrated, the high density layer 18 is disposed over theadhesion layer 20.

In certain applications, the high density metal strip layer 18 of themetal strip 16 can include any suitable metal that has a mass densitythat is equal to or greater than the mass density of the IDT electrode12 or any suitable material that provides sufficient mass loading with asuitable dimension. For example, the high density metal strip layer 18can include molybdenum (Mo), tungsten (W), gold (Au), silver (Ag),ruthenium (Ru), copper (Cu), platinum (Pt), iridium (Ir) or the like.Moreover, in some applications, a multi-layer mass loading strip caninclude a high density non-conductive layer in place of the high densitymetal strip layer 18. Such a high density non-conductive layer can be aheavy dielectric layer such as tantalum pentoxide (Ta₂O₅), telluriumdioxide (TeO₂), or the like dielectric material.

The adhesion layer 20 of the metal strip 16 can provide a betteradhesion with the temperature compensation layer 14 than the adhesionbetween the high density metal strip layer 18 with the temperaturecompensation layer 14. For example, the adhesion layer 20 can includetitanium (Ti), titanium nitride (TiN), aluminum nitride (AlN), tantalumpentoxide (Ta₂O₅), or the like. Some materials, such as Ti, for theadhesion layer 20 can improve a crystal orientation of the high densitymetal strip layer 18 than the metal strip 16 with different material forthe adhesion layer 20 or without the adhesion layer 20. Accordingly, incertain applications, the adhesion layer 20 can be a titanium layer thatprovides desirable adhesion and desirable crystal orientation. The metalstrip 16 may be formed in any suitable manner. For example, the adhesionlayer 20 may be provided over the temperature compensation layer 14 byway of deposition. For example, the high density metal strip 18 may beprovided over the adhesion layer 20 by way of deposition. An adhesionlayer in a multi-layer mass loading strip can be non-conductive incertain applications.

The metal strip 16 has a thickness t3. The thickness t3 of the metalstrip 16 can be the sum of a thickness t4 of the high density metalstrip layer 18 and a thickness t5 of the adhesion layer 20. Thethickness t4 of the high density metal strip layer 18 can be selectedbased on a wavelength λ or L of a surface acoustic wave generated by thesurface acoustic wave resonator 1. For example, the thickness t4 of thehigh density metal strip layer 18 can be in a range from 0.01 L to 0.03L. The adhesion layer 20 can have any suitable thickness t5 that canprovide an improved adhesion as compared to the metal strip 16 withoutthe adhesion layer 20. For example, the thickness t5 can be less than 50nm. Preferably, in order to provide an improved crystal orientation, thethickness t5 of the adhesion layer 20 can be in a range from 10 nm to 50nm.

The metal strip 16 has an inner edge 16 a and an outer edge 16 b. Theouter edge 16 b of the metal strip 16 are illustrated to be aligned withthe distal ends 22 b of the fingers 22. However, in some embodiments,the outer edge 16 b can be anywhere between the distal end 22 b of thefinger 22 that extends from the bus bar 24 and the bus bar 24. In someother embodiments, the outer edge 16 b may overlap with the bus bar 24or be outside of the IDT electrode 12.

FIG. 1D illustrates a cross section of a surface acoustic wave (SAW)resonator 1′ according to an embodiment. The SAW resonator 1′ includes apiezoelectric layer 10, an IDT electrode 12 over the piezoelectric layer10, a temperature compensation layer 14 over the IDT electrode 12, and ametal strip 16′ buried in the temperature compensation layer 14. FIG. 1Eillustrates a top view of the SAW resonator 1′ of FIG. 1D. FIG. 1Fillustrates a side view of the metal strip 16′ of FIG. 1D. The SAWresonator 1′ is generally similar to the SAW resonator 1 illustrated inFIGS. 1A to 1C, except that the metal strip 16′ of the SAW resonator 1′includes three layers. A multi-layer metal strip in accordance with theprinciples and advantages disclosed herein can include more than threelayers in some other embodiments.

As illustrated in FIG. 1F, the metal strip 16′ includes a first layer(e.g., an adhesion layer 20), a second layer (e.g., a high density metalstrip layer 18), and a third layer 19. The third layer 19 can be asecond adhesion layer. This can provide a better adhesion with thetemperature compensation layer 14 than the adhesion between the highdensity metal strip layer 18 with the temperature compensation layer 14.The second adhesion layer can be a titanium layer. In certain instances,the adhesion layer 20 and the second adhesion layer 19 can be of thesame material. For example, the metal strip 16′ can be a titanium/highdensity metal/titanium strip. The second adhesion layer can includetitanium nitride (TiN), aluminum nitride (AlN), tantalum pentoxide(Ta₂O₅), or the like in some other instances.

FIG. 1G illustrates a cross section of a SAW resonator 1″ according toanother embodiment. The SAW resonator 1″ is like the SAW resonator 1 ofFIG. 1A except that the SAW resonator 1″ additionally includes a supportsubstrate 21 on a side of the piezoelectric layer 10 that is opposite tothe IDT electrode structure 12. FIG. 1G illustrates that a metal strip16 can be implemented in a SAW resonator with a multi-layerpiezoelectric substrate. In certain applications, the piezoelectriclayer 21 can have a thickness of less than the pitch λ, of the IDTelectrode 12 in the SAW resonator 1″ Such a piezoelectric layer can havea thickness in a range from about 0.1λ to 1λ. For example, thepiezoelectric layer 21 can have a thickness in a range from about 0.1λto 0.4λ. In some other applications, the piezoelectric layer 21 can havea thickness in a range from about 1λ to 40λ of the pitch λ of IDTelectrode 12 in the SAW resonator 1″. In certain instances, thethickness of the piezoelectric layer 21 can be in a range from 0.1micrometer to 30 micrometers.

The support substrate 21 can be any suitable substrate layer, such as asilicon layer, a quartz layer, a ceramic layer, a glass layer, a spinellayer, a magnesium oxide spinel layer, a sapphire layer, a diamondlayer, a silicon carbide layer, a silicon nitride layer, an aluminumnitride layer, or the like. As one example, the SAW resonator 1″ caninclude a lithium niobate/silicon piezoelectric substrate in certainapplications.

The support substrate 21 can have a relatively high acoustic impedance.An acoustic impedance of the support substrate 21 can be higher than anacoustic impedance of the piezoelectric layer 10. For instance, thesupport substrate 21 can have a higher acoustic impedance than anacoustic impedance of lithium niobate and a higher acoustic impedancethan lithium tantalate. The acoustic impedance of the support substrate21 can be higher than an acoustic impedance of the temperaturecompensation layer 21. The SAW resonator 1″ including the piezoelectriclayer 10 on a support substrate 21 with relatively high thermalconductivity, such as silicon substrate, can achieve better thermaldissipation compared to a similar SAW resonator without the highimpedance support substrate 21.

In certain embodiments, a SAW resonator can include two or more layerson the side of the piezoelectric layer 10 that is opposite to the IDTelectrode 12. In some embodiments, there can be an additional layerbetween the piezoelectric layer 10 and the support substrate 21. Theadditional layer can be a low impedance layer that has a lower acousticimpedance than the support substrate 12. In some embodiments, theadditional layer can be a silicon dioxide (SiO2) layer. The additionallayer can increase adhesion between layers of the multi-layerpiezoelectric substrate. In such applications, the additional layer canbe referred to as an adhesion layer. Alternatively or additionally, theadditional layer can increase heat dissipation in the SAW resonatorrelative to the SAW resonator 1, 1″. In such applications, theadditional layer can be referred to as a heat dissipation layer. Theadditional layer can reduce back reflection of the support substrate incertain applications. In such applications, the additional layer canscatter back reflections by beam scattering. In some instances, theadditional layer can be a polycrystalline spinel layer and the supportsubstrate 12 can be a silicon layer.

In some other embodiments, a multi-layer mass loading strip can includetwo or more layers of high density metal. The high density metal layerscan be of different high density material. Example high density metalsinclude molybdenum (Mo), tungsten (W), gold (Au), silver (Ag), ruthenium(Ru), copper (Cu), platinum (Pt), iridium (Ir) or the like.

FIG. 1H illustrates a cross section of a surface acoustic wave (SAW)resonator 1′″ according to an embodiment. FIG. 1I illustrates a top viewof the SAW resonator 1′″ of FIG. 1H along the line 1H-1H in FIG. 1I. TheSAW resonator 1′″ of FIGS. 1H and 1I is like the SAW resonator 1 ofFIGS. 1A and 1B, except that the metal strip 16 of the SAW resonator 1′″is offset or shifted by a displacement distance d. Even through themetal strip 16 is shifted in the SAW resonator 1′″, the metal strip 16overlaps the edge portions of fingers 22 in the SAW resonator 1′″. FIGS.1H and 1I illustrate that a mass loading strip can overlap the edgeportions of fingers of an IDT electrode in cases where the fingers 22extend a relatively small amount beyond the mass loading strip.

As illustrated, the metal strip 16 can be positioned over edge portionnear the distal portion 22 b of a finger 22. In some applications, thedisplacement distance d can be up to 0.1λ. For example, the displacementd can be in a range from 0.01λ to 0.1λ. In some applications, thedisplacement d can be up to 400 nm. For example, the displacement d canbe in a range from 10 nm to 400 nm. With such displacements, theperformance of the SAW resonator 1′″ should not be significantlydegraded relative to the SAW resonator 1.

FIG. 2 illustrates a cross section of a surface acoustic wave (SAW)resonator 2 according to an embodiment. The resonator 2 illustrated inFIG. 2 is generally similar to the resonator 1 illustrated in FIG. 1A.However, unlike the IDT electrode 12 of the resonator 1 illustrated inFIG. 1A, the IDT electrode 13 of the resonator 2 illustrated in FIG. 2includes a plurality of conductive layers. As illustrated, the IDTelectrode of the resonator 2 includes a molybdenum (Mo) layer 26 and analuminum (Al) layer 28. The Mo layer 26 of the IDT electrode 13 has athickness t6. In some embodiments, the thickness t6 of the Mo layer 26can be about 0.05 L. For example, when the wavelength L is 4 μm, thethickness t6 of the Mo layer 26 can be 200 nm.

FIG. 3 illustrates a cross section of a surface acoustic wave (SAW)resonator 3 according to an embodiment. The resonator 3 illustrated inFIG. 3 is generally similar to the resonator 1 illustrated in FIG. 1A.However, unlike the metal strip 16 of the resonator 1 that includes thehigh density metal strip layer 18 and the adhesion layer 20, the metalstrip of the SAW resonator 3 includes only the high density metal striplayer 18. FIG. 3 illustrates a delamination of the high density metalstrip layer 18. This can be due to a relatively weak adhesion betweenthe high density metal strip layer 18 and the temperature compensationlayer 14. The delamination of the high density metal strip layer 18 cancause transverse modes.

FIG. 4A is a graph showing a measurement of admittance of the SAWresonator 3 of FIG. 3. FIG. 4B is a graph showing a measurement ofadmittance of a resonator similar to the SAW resonator 3 illustrated inFIG. 3 without the metal strip layer 18 being delaminated. The graph canindicate that the metal strip layer 18, when not delaminated, cansuppress transverse modes. On the other hand, transverse modes near andbetween resonance and anti-resonance (e.g., in a region 30) are observedin FIG. 4A. This can be due to the delamination of the high densitymetal strip layer 18 illustrated in FIG. 3. Accordingly, suchdelamination can provide an undesirable frequency response for the SAWresonator 3.

FIG. 4C is a graph showing a measurement of admittance of the SAWresonator 1 of FIG. 1A. The graph can indicate that the metal strip 16can suppress transverse mode as much as or more than the metal striplayer 18. Therefore, the metal strip 16 can provide transversesuppression while having a relatively strong adhesion with thetemperature compensation layer 14.

FIG. 5 illustrates a cross section of a portion of a surface acousticwave (SAW) resonator 4 according to an embodiment. The resonator 4illustrated in FIG. 5 is generally similar to the resonator 1illustrated in FIG. 1A. However, unlike the resonator 1 illustrated inFIG. 1A, the resonator 4 includes a silicon nitride (SiN) layer 32 overthe temperature compensation layer 14. The SiN layer 32 can be disposedentirely or partially over an upper surface 14 b of the temperaturecompensation layer 14. In some instances, an IDT electrode can includefingers having the SiN layer 32 over a central portion of an activeregion and border regions free from SiN. The SiN layer 32 can cause amagnitude of the velocity in the underlying region of the SAW resonator4 to be increased. In certain applications, another suitable materialcan be implemented in place of the SiN layer 32 to increase themagnitude of the velocity of the underlying region of the SAW resonator4.

As with the resonators 1 and 2 illustrated in FIGS. 1A and 2,respectively, the metal strip 16 can include a plurality of layers, suchas, a high density metal strip layer and an adhesion layer. The metalstrip 16 can be disposed at any suitable position that is a distance rfrom the piezoelectric layer 10 (or from the lower surface 14 a of thetemperature compensation layer 14). The distance r may be selectedrelative to the thickness t1 of the temperature compensation layer 14.For example, the distance r can be in a range from 0.2×t1 to 0.8×t1 insome embodiments, in which t1 is the thickness of the temperaturecompensation layer 14. When the SiN layer 32 is disposed over thetemperature compensation layer 14, it may be preferable for the distancer to be in a range from 0.4×t1 to 0.6×t1.

FIG. 6 is a graph showing simulated velocities of a surface acousticwave in surface acoustic wave (SAW) resonators. First simulation results34 are for the resonator with a metal strip that includes only Ti (Timetal strip) and second simulation results 36 are for the resonator witha metal strip that includes only Mo (Mo metal strip). As shown in FIG.6, Ti provides less mass loading than Mo for the same thickness. Forexample, a specified mass loading ΔV for a piston operation may be about105 m/s. The resonator with the Mo metal strip having a thickness about0.015 L can obtain the specified mass loading ΔV of 105 m/s. However, atthe same thickness, the resonator with the Ti metal strip obtains a massloading of about 25 m/s. For the piston mode operation to suppress thetransverse mode efficiently, the specified mass loading ΔV is preferablyset in a range from 40 m/s to 120 m/s. In order to obtain the specifiedmass loading ΔV, the thickness of the Ti metal strip should be thicker(e.g., about 3.7 times thicker) than the Mo metal strip. Fabricating arelatively thick Ti metal strip can be challenging. Therefore, it can bebeneficial to use the Mo in the metal strip for mass loading.

The mass loading strips disclosed herein can be implemented togetherwith a piston mode structure of an IDT electrode and/or with anoverlying layer arranged to adjust acoustic velocity in an underlyingregion of an acoustic wave device.

FIG. 7A illustrates a cross section of a surface acoustic wave (SAW)resonator 5 according to an embodiment. The SAW resonator 5 includes apiezoelectric layer 10, an IDT electrode 12′ over the piezoelectriclayer 10, a temperature compensation layer 14 over the IDT electrode12′, and a metal strip 16 buried in the temperature compensation layer14.

FIG. 7B illustrates a top view of the SAW resonator 5 of FIG. 7A. Eachfinger 22′ has a proximate end 22 a′ that is in contact with a bus bar24 and a distal end 22 b′ opposite the proximate end 22 a′. A bodyportion 22 c′ of the finger 22′ extends between the proximate end 22 a′and the distal end 22 b′. A portion near the distal end 22 b′ can bereferred as an edge portion. The SAW resonator 5 is generally similar tothe SAW resonator 1 illustrated in FIGS. 1A to 1C, except that thedistal ends 22 b′ of the fingers of the IDT electrode 12′ of the SAWresonator 5 have a hammer head shape. The hammer head distal end 22 b′can provide a velocity difference between the border region and acentral part of the active region, thereby facilitating the piston modeoperation.

FIG. 8A illustrates a cross section of a surface acoustic wave (SAW)resonator 6 according to an embodiment. The SAW resonator 6 includes apiezoelectric layer 10, an IDT electrode 12″ over the piezoelectriclayer 10, a temperature compensation layer 14 over the IDT electrode12″, and a metal strip 16 buried in the temperature compensation layer14.

FIG. 8B illustrates a top view of the SAW resonator 6 of FIG. 8A. Eachfinger 22″ has a proximate end 22 a″ that is in contact with a bus bar24 and a distal end 22 b″ opposite the proximate end 22 a″. A bodyportion 22 c″ of the finger 22″ extends between the proximate end 22 a″and the distal end 22 b″. A portion near the distal end 22 b″ can bereferred as an edge portion. The SAW resonator 6 is generally similar tothe SAW resonator 5 illustrated in FIGS. 7A and 7B, except that the bodyportion 22 c″ of fingers of the IDT electrode 12″ of the SAW resonator 6has a widened portion 40. The widened portion 40 can provide a velocitydifference between the border region and a central part of the activeregion, thereby facilitating the piston mode operation.

FIG. 9A illustrates a cross section of a surface acoustic wave (SAW)resonator 7 according to an embodiment. The SAW resonator 7 includes apiezoelectric layer 10, an IDT electrode 12′″ over the piezoelectriclayer 10, a temperature compensation layer 14 over the IDT electrode12′″, and a metal strip 16 buried in the temperature compensation layer14.

FIG. 9B illustrates a top view of the SAW resonator 6 of FIG. 9A. TheSAW resonator 7 is generally similar to the SAW resonator 5 illustratedin FIGS. 7A and 7B, except that the bus bar 24′ of the IDT electrode12′″ of the SAW resonator 7 includes an extension portion 42. Theextension portion 42 can provide a velocity difference between theborder region and a central part of the active region, therebyfacilitating the piston mode operation.

FIG. 10A illustrates a cross section of a surface acoustic wave (SAW)resonator 8 according to an embodiment. The SAW resonator 8 includes apiezoelectric layer 10, an IDT electrode 12″″ over the piezoelectriclayer 10, a temperature compensation layer 14 over the IDT electrode12″″, and a metal strip 16 buried in the temperature compensation layer14.

FIG. 10B illustrates a top view of the SAW resonator 6 of FIG. 10A. TheSAW resonator 8 is generally similar to the SAW resonator 7 illustratedin FIGS. 9A and 9B, except that the IDT electrode 12″″ of the SAWresonator 8 includes a widened portion 44. The widened portion 44 canprovide a velocity difference between the border region and a centralpart of the active region, thereby facilitating the piston modeoperation.

FIG. 11A illustrates a cross section of a surface acoustic wave (SAW)resonator 9 according to an embodiment. The SAW resonator 9 includes apiezoelectric layer 10, an IDT electrode 12 over the piezoelectric layer10, a temperature compensation layer 14 over the IDT electrode 12′, ametal strip 16 buried in the temperature compensation layer 14, and apassivation layer 46 over the temperature compensation layer 14.

FIG. 11B illustrates a top view of the SAW resonator 9 of FIG. 11A. TheSAW resonator 9 is generally similar to the SAW resonator 1 illustratedin FIGS. 1A to 1C, except that the SAW resonator 9 includes thepassivation layer 46.

The illustrated passivation layer 46 is disposed entirely over an uppersurface of the temperature compensation layer 14 in the illustratedcross section. However, the passivation layer 46 can be disposedpartially over the upper surface of the temperature compensation layer14 with one or more trenches, in some other instances. In someembodiments, the passivation layer 46 can be a dispersion adjustmentlayer. The dispersion adjustment layer can cause a magnitude of thevelocity in the underlying region of the SAW resonator 9 to beincreased. In certain applications, the passivation layer 46 can includeany suitable material to increase the magnitude of the velocity of theunderlying region of the SAW resonator 9. According in someapplications, the passivation layer 46 can include silicon nitride(SiN). In some embodiments, the passivation layer 46 can be patternedsuch that the acoustic propagation velocity can be adjusted at certainregions of the SAW resonator 9. For example, the passivation layer 46can have a trench. The trench can be positioned over the conductivestrip in certain embodiments to decrease acoustic velocity in a borderregion to thereby provide transverse mode suppression.

FIG. 12A illustrates a cross section of a surface acoustic wave (SAW)resonator 11 according to an embodiment. The SAW resonator 11 includes apiezoelectric layer 10, an IDT electrode 12 over the piezoelectric layer10, a temperature compensation layer 14 over the IDT electrode 12, and ametal strip 16 disposed on the temperature compensation layer 14.

FIG. 12B illustrates a top view of the SAW resonator 11 of FIG. 12A. TheSAW resonator 11 is generally similar to the SAW resonator 1 illustratedin FIGS. 1A to 1C, except that the metal strip 16 of the SAW resonator 9is disposed on the temperature compensation layer 14. In somemanufacturing processes, it can be easier to manufacture a SAW resonatorthat has a metal strip 16 on top of the temperature compensation layerthan having the metal strip embedded in the temperature compensationlayer.

FIG. 13A illustrates a cross section of a Lamb wave device 15 accordingto an embodiment. The Lamb wave device 15 can be a Lamb wave resonator.The Lamb wave device 15 includes a piezoelectric layer 10, an IDTelectrode 12 over the piezoelectric layer 10, a temperature compensationlayer 14 over the IDT electrode 12, and a metal strip 16 buried in thetemperature compensation layer 14. The illustrated metal strip 16includes a high density metal strip layer 18 and an adhesion layer 20.Accordingly, the metal strip 16 is a multi-layer conductive strip. Amulti-layer metal strip can include three or more layers in some otherembodiments. The multi-layer metal strip 16 performs a mass loadingfunction. Accordingly, the multi-layer metal strip 16 is an example of amulti-layer mass loading strip. The Lamb wave device 15 also includes asubstrate 25, and an air cavity 27 formed between the piezoelectriclayer 10 and the substrate 25. The substrate 25 can include any suitablematerial. For example, the substrate 25 can be a semiconductorsubstrate, such as a silicon substrate.

FIG. 13B illustrates a cross section of a Lamb wave device 17 accordingto another embodiment. The Lamb wave device 17 can be a Lamb waveresonator. The Lamb wave device 17 is like the Lamb wave device 15 ofFIG. 13A except that the Lamb wave device 17 includes a solid acousticmirror 29 and a substrate 31 in place of the substrate 25 and the cavity27. The solid acoustic mirror 29 can include Bragg reflectors. Forinstance, the solid acoustic mirror 29 can include alternating layers ofa low impedance layer 29 a and a high impedance layer 29 b. As oneexample, the low impedance layer can be a silicon dioxide layer and thehigh impedance layer can be a tungsten layer. The substrate 31 caninclude any suitable material. For example, the substrate 31 can be asemiconductor substrate, such as a silicon substrate.

A method of manufacturing an acoustic wave resonator according to anembodiment will now be described. The method can include providing anacoustic wave resonator with a temperature compensation layer over aninterdigital transducer electrode. The interdigital transducer electrodeincludes fingers extending from a bus bar. The fingers each include anedge portion and a body portion. The method includes forming a firstlayer of a mass loading strip that overlaps with the edge portions ofthe fingers of the interdigital transducer electrode. Material of thetemperature compensation layer is positioned between the first layer ofthe mass loading strip and the interdigital transducer electrode. Themethod also includes depositing a second layer of the mass loading stripover the first layer of the mass loading strip. The first layer of themass loading strip has a higher adhesion than the second layer of themass loading strip. The second layer of the mass loading strip has ahigher mass than the first layer of the mass loading strip.

A method of filtering a radio frequency signal according to anembodiment will now be described. The method includes receiving a radiofrequency signal at an input port of an acoustic wave filter thatincludes an acoustic wave resonator. The acoustic wave resonatorincludes a multi-layer mass loading strip that overlaps edge portions offingers of an interdigital transducer electrode. The method alsoincludes filtering the radio frequency signal with the acoustic wavefilter. The filtering includes suppressing a transverse mode using themulti-layer mass loading strip of the acoustic wave resonator. Thefiltering can be performed, for example, with the transmit filter 45 ofFIG. 14A or the receive filter 50 of FIG. 14B.

A SAW device including any suitable combination of features disclosedherein be included in a filter arranged to filter a radio frequencysignal in a fifth generation (5G) New Radio (NR) operating band withinFrequency Range 1 (FR1). A filter arranged to filter a radio frequencysignal in a 5G NR operating band can include one or more SAW devicesdisclosed herein. FR1 can be from 410 MHz to 7.125 GHz, for example, asspecified in a current 5G NR specification. One or more SAW devices inaccordance with any suitable principles and advantages disclosed hereincan be included in a filter arranged to filter a radio frequency signalin a 4G LTE operating band and/or in a filter having a passband thatincludes a 4G LTE operating band and a 5G NR operating band.

FIG. 14A is a schematic diagram of an example transmit filter 45 thatincludes surface acoustic wave resonators of a surface acoustic wavecomponent according to an embodiment. The transmit filter 45 can be aband pass filter. The illustrated transmit filter 45 is arranged tofilter a radio frequency signal received at a transmit port TX andprovide a filtered output signal to an antenna port ANT. The transmitfilter 45 includes series SAW resonators TS1, TS2, TS3, TS4, TS5, TS6,and TS7, shunt SAW resonators TP1, TP2, TP3, TP4, and TP5, series inputinductor L1, and shunt inductor L2. Some or all of the SAW resonatorsTS1 to TS7 and/or TP1 to TP5 can be a SAW resonators with a multi-layermass loading strip for transverse mode suppression in accordance withany suitable principles and advantages disclosed herein. For instance,one or more of the SAW resonators of the transmit filter 45 can be asurface acoustic wave resonator 1 of FIGS. 1A to 1C. Alternatively oradditionally, one or more of the SAW resonators of the transmit filter45 can be a surface acoustic wave resonator 2 of FIG. 2 and/or a surfaceacoustic wave resonator 4 of FIG. 5. Any suitable number of series SAWresonators and shunt SAW resonators can be included in a transmit filter45.

FIG. 14B is a schematic diagram of a receive filter 50 that includessurface acoustic wave resonators of a surface acoustic wave componentaccording to an embodiment. The receive filter 50 can be a band passfilter. The illustrated receive filter 50 is arranged to filter a radiofrequency signal received at an antenna port ANT and provide a filteredoutput signal to a receive port RX. The receive filter 50 includesseries SAW resonators RS1, RS2, RS3, RS4, RS5, RS6, RS7, and RS7, shuntSAW resonators RP1, RP2, RP3, RP4, and RP5, and RP6, shunt inductor L2,and series output inductor L3. Some or all of the SAW resonators RS1 toRS8 and/or RP1 to RP6 can be SAW resonators with a multi-layer massloading strip for transverse mode suppression in accordance with anysuitable principles and advantages disclosed herein. For instance, oneor more of the SAW resonators of the receive filter 50 can be a surfaceacoustic wave resonator 1 of FIGS. 1A to 1C. Alternatively oradditionally, one or more of the SAW resonators of the receive filter 50can be a surface acoustic wave resonator 2 of FIG. 2 and/or a surfaceacoustic wave resonator 4 of FIG. 5. Any suitable number of series SAWresonators and shunt SAW resonators can be included in a receive filter50.

FIG. 15 is a schematic diagram of a radio frequency module 75 thatincludes a surface acoustic wave component 76 according to anembodiment. The illustrated radio frequency module 75 includes the SAWcomponent 76 and other circuitry 77. The SAW component 76 can includeone or more SAW devices with any suitable combination of features of theSAW devices disclosed herein. Such SAW devices can include one or moreSAW resonators, one or more SAW delay lines, one or more multi-mode SAWfilters, or any suitable combination thereof. The SAW component 76 caninclude a SAW die that includes SAW resonators.

The SAW component 76 shown in FIG. 15 includes a filter 78 and terminals79A and 79B. The filter 78 includes SAW resonators. One or more of theSAW resonators can be implemented in accordance with any suitableprinciples and advantages of the surface acoustic wave resonator 1 ofFIGS. 1A to 1C, the surface acoustic wave resonator 2 of FIG. 2 and/or asurface acoustic wave resonator 4 of FIG. 5. The filter 78 can be aTC-SAW filter arranged as a band pass filter to filter radio frequencysignals with frequencies below about 3.5 GHz in certain applications.The terminals 79A and 78B can serve, for example, as an input contactand an output contact. The SAW component 76 and the other circuitry 77are on a common packaging substrate 80 in FIG. 15. The package substrate80 can be a laminate substrate. The terminals 79A and 79B can beelectrically connected to contacts 81A and 81B, respectively, on thepackaging substrate 80 by way of electrical connectors 82A and 82B,respectively. The electrical connectors 82A and 82B can be bumps or wirebonds, for example. The other circuitry 77 can include any suitableadditional circuitry. For example, the other circuitry can include oneor more power amplifiers, one or more radio frequency switches, one ormore additional filters, one or more low noise amplifiers, the like, orany suitable combination thereof. The radio frequency module 75 caninclude one or more packaging structures to, for example, provideprotection and/or facilitate easier handling of the radio frequencymodule 75. Such a packaging structure can include an overmold structureformed over the packaging substrate 75. The overmold structure canencapsulate some or all of the components of the radio frequency module75.

FIG. 16 is a schematic diagram of a radio frequency module 84 thatincludes a surface acoustic wave component according to an embodiment.As illustrated, the radio frequency module 84 includes duplexers 85A to85N that include respective transmit filters 86A1 to 86N1 and respectivereceive filters 86A2 to 86N2, a power amplifier 87, a select switch 88,and an antenna switch 89. The radio frequency module 84 can include apackage that encloses the illustrated elements. The illustrated elementscan be disposed on a common packaging substrate 80. The packagingsubstrate can be a laminate substrate, for example.

The duplexers 85A to 85N can each include two acoustic wave filterscoupled to a common node. The two acoustic wave filters can be atransmit filter and a receive filter. As illustrated, the transmitfilter and the receive filter can each be band pass filters arranged tofilter a radio frequency signal. One or more of the transmit filters86A1 to 86N1 can include one or more SAW resonators in accordance withany suitable principles and advantages disclosed herein. Similarly, oneor more of the receive filters 86A2 to 86N2 can include one or more SAWresonators in accordance with any suitable principles and advantagesdisclosed herein. Although FIG. 16 illustrates duplexers, any suitableprinciples and advantages disclosed herein can be implemented in othermultiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/orin switch-plexers.

The power amplifier 87 can amplify a radio frequency signal. Theillustrated switch 88 is a multi-throw radio frequency switch. Theswitch 88 can electrically couple an output of the power amplifier 87 toa selected transmit filter of the transmit filters 86A1 to 86N1. In someinstances, the switch 88 can electrically connect the output of thepower amplifier 87 to more than one of the transmit filters 86A1 to86N1. The antenna switch 89 can selectively couple a signal from one ormore of the duplexers 85A to 85N to an antenna port ANT. The duplexers85A to 85N can be associated with different frequency bands and/ordifferent modes of operation (e.g., different power modes, differentsignaling modes, etc.).

FIG. 17A is a schematic diagram of a wireless communication 90 devicethat includes filters 93 in a radio frequency front end 92 according toan embodiment. The filters 93 can include one or more SAW resonators inaccordance with any suitable principles and advantages discussed herein.The wireless communication device 90 can be any suitable wirelesscommunication device. For instance, a wireless communication device 90can be a mobile phone, such as a smart phone. As illustrated, thewireless communication device 90 includes an antenna 91, an RF front end92, a transceiver 94, a processor 95, a memory 96, and a user interface97. The antenna 91 can transmit RF signals provided by the RF front end92. Such RF signals can include carrier aggregation signals. Althoughnot illustrated, the wireless communication device 90 can include amicrophone and a speaker in certain applications.

The RF front end 92 can include one or more power amplifiers, one ormore low noise amplifiers, one or more RF switches, one or more receivefilters, one or more transmit filters, one or more duplex filters, oneor more multiplexers, one or more frequency multiplexing circuits, thelike, or any suitable combination thereof. The RF front end 92 cantransmit and receive RF signals associated with any suitablecommunication standards. The filters 93 can include SAW resonators of aSAW component that includes any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

The transceiver 94 can provide RF signals to the RF front end 92 foramplification and/or other processing. The transceiver 94 can alsoprocess an RF signal provided by a low noise amplifier of the RF frontend 92. The transceiver 94 is in communication with the processor 95.The processor 95 can be a baseband processor. The processor 95 canprovide any suitable base band processing functions for the wirelesscommunication device 90. The memory 96 can be accessed by the processor95. The memory 96 can store any suitable data for the wirelesscommunication device 90. The user interface 97 can be any suitable userinterface, such as a display with touch screen capabilities.

FIG. 17B is a schematic diagram of a wireless communication device 100that includes filters 93 in a radio frequency front end 92 and a secondfilter 103 in a diversity receive module 102. The wireless communicationdevice 100 is like the wireless communication device 90 of FIG. 17A,except that the wireless communication device 100 also includesdiversity receive features. As illustrated in FIG. 17B, the wirelesscommunication device 100 includes a diversity antenna 101, a diversitymodule 102 configured to process signals received by the diversityantenna 101 and including filters 103, and a transceiver 104 incommunication with both the radio frequency front end 92 and thediversity receive module 102. The filters 103 can include one or moreSAW resonators that include any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

Although embodiments disclosed herein relate to surface acoustic waveresonators, any suitable principles and advantages disclosed herein canbe applied to other types of acoustic wave resonators, such as Lamb waveresonators and/or boundary wave resonators. For example, any suitablecombination of features of the multi-layer mass loading strips disclosedherein can be applied to a Lamb wave resonator and/or a boundary waveresonator.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includessome example embodiments, the teachings described herein can be appliedto a variety of structures. Any of the principles and advantagesdiscussed herein can be implemented in association with RF circuitsconfigured to process signals in a frequency range from about 30 kHz to300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as packaged radio frequency modules, uplinkwireless communication devices, wireless communication infrastructure,electronic test equipment, etc. Examples of the electronic devices caninclude, but are not limited to, a mobile phone such as a smart phone, awearable computing device such as a smart watch or an ear piece, atelephone, a television, a computer monitor, a computer, a modem, ahand-held computer, a laptop computer, a tablet computer, a microwave, arefrigerator, a vehicular electronics system such as an automotiveelectronics system, a stereo system, a digital music player, a radio, acamera such as a digital camera, a portable memory chip, a washer, adryer, a washer/dryer, a copier, a facsimile machine, a scanner, amulti-functional peripheral device, a wrist watch, a clock, etc.Further, the electronic devices can include unfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” and words of similar import, when usedin this application, shall refer to this application as a whole and notto any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. An acoustic wave device comprising: apiezoelectric layer; an interdigital transducer electrode over thepiezoelectric layer, the interdigital transducer electrode including abus bar and a plurality of fingers extending from the bus bar, theplurality of fingers each including an edge portion and a body portion;a temperature compensation layer over the interdigital transducerelectrode; and a mass loading strip overlapping the edge portions of theplurality of fingers, the mass loading strip having a density that ishigher than a density of the temperature compensation layer, the massloading strip including a first layer and a second layer, a portion ofthe temperature compensation layer being positioned between the massloading strip and the piezoelectric layer, the mass loading striparranged to suppress a transverse mode, the first layer of the massloading strip positioned between the second layer of the mass loadingstrip and the interdigital transducer electrode, and the first layer ofthe mass loading strip having higher adhesion to the temperaturecompensation layer than the second layer of the mass loading strip. 2.The acoustic wave device of claim 1 wherein the temperature compensationlayer has a thickness from a lower surface to an upper surface oppositethe lower surface, and the mass loading strip is spaced apart from thelower surface by a distance that is within 40% to 60% of the thicknessof the temperature compensation layer.
 3. The acoustic wave device ofclaim 1 wherein the second layer of the mass loading strip has a highermass than the first layer of the mass loading strip.
 4. The acousticwave device of claim 1 wherein the second layer of the mass loadingstrip is a conductive strip.
 5. An acoustic wave device comprising: apiezoelectric layer; an interdigital transducer electrode over thepiezoelectric layer, the interdigital transducer electrode including abus bar and a plurality of fingers extending from the bus bar, theplurality of fingers each including an edge portion and a body portion;a temperature compensation layer over the interdigital transducerelectrode; and a mass loading strip overlapping the edge portions of theplurality of fingers, the mass loading strip having a density that ishigher than a density of the temperature compensation layer, the massloading strip including a first layer and a second layer, a portion ofthe temperature compensation layer being positioned between the massloading strip and the piezoelectric layer, the mass loading striparranged to suppress a transverse mode, the first layer of the massloading strip positioned between the second layer of the mass loadingstrip and the interdigital transducer electrode, and the first layer ofthe mass loading strip including titanium.
 6. The acoustic wave deviceof claim 5 wherein the second layer of the mass loading strip includesmolybdenum.
 7. An acoustic wave device comprising: a piezoelectriclayer; an interdigital transducer electrode over the piezoelectriclayer, the interdigital transducer electrode including a bus bar and aplurality of fingers extending from the bus bar, the plurality offingers each including an edge portion and a body portion; a temperaturecompensation layer over the interdigital transducer electrode; and amass loading strip overlapping the edge portions of the plurality offingers, the mass loading strip having a density that is higher than adensity of the temperature compensation layer, the mass loading stripincluding a first layer and a second layer, a portion of the temperaturecompensation layer being positioned between the mass loading strip andthe piezoelectric layer, the mass loading strip arranged to suppress atransverse mode, the first layer of the mass loading strip positionedbetween the second layer of the mass loading strip and the interdigitaltransducer electrode, and the second layer of the mass loading striphaving a mass sufficient to suppress the transverse mode.
 8. An acousticwave device comprising: a piezoelectric layer; an interdigitaltransducer electrode over the piezoelectric layer, the interdigitaltransducer electrode including a bus bar and a plurality of fingersextending from the bus bar, the plurality of fingers each including anedge portion and a body portion; a temperature compensation layer overthe interdigital transducer electrode; and a mass loading stripoverlapping the edge portions of the plurality of fingers, the massloading strip having a density that is higher than a density of thetemperature compensation layer, the mass loading strip including a firstlayer and a second layer, a portion of the temperature compensationlayer being positioned between the mass loading strip and thepiezoelectric layer, the mass loading strip arranged to suppress atransverse mode, and the mass loading strip embedded in the temperaturecompensation layer.
 9. The acoustic wave device of claim 8 wherein theacoustic wave device is configured to generate a surface acoustic wave.10. The acoustic wave device of claim 8 wherein the temperaturecompensation layer is a silicon dioxide layer.
 11. An acoustic wavedevice comprising: a piezoelectric layer; an interdigital transducerelectrode over the piezoelectric layer, the interdigital transducerelectrode including a bus bar and a plurality of fingers extending fromthe bus bar, the plurality of fingers each including an edge portion anda body portion; a temperature compensation layer over the interdigitaltransducer electrode the temperature compensation layer having athickness from a lower surface to an upper surface opposite the lowersurface; and a mass loading strip overlapping the edge portions of theplurality of fingers, the mass loading strip having a density that ishigher than a density of the temperature compensation layer, the massloading strip including a first layer and a second layer, a portion ofthe temperature compensation layer being positioned between the massloading strip and the piezoelectric layer, the mass loading striparranged to suppress a transverse mode, and the mass loading stripspaced apart from the lower surface by a distance that is within 20% to80% of the thickness of the temperature compensation layer.
 12. Anacoustic wave device comprising: a piezoelectric layer; an interdigitaltransducer electrode over the piezoelectric layer, the interdigitaltransducer electrode including a bus bar and a plurality of fingersextending from the bus bar, the plurality of fingers each including anedge portion and a body portion; a temperature compensation layer overthe interdigital transducer electrode; and a mass loading stripoverlapping the edge portions of the plurality of fingers, the massloading strip having a density that is higher than a density of thetemperature compensation layer, the mass loading strip including a firstlayer and a second layer, a portion of the temperature compensationlayer being positioned between the mass loading strip and thepiezoelectric layer, the mass loading strip arranged to suppress atransverse mode, and the second layer having a higher density than adensity of the interdigital transducer electrode.
 13. An acoustic wavedevice comprising: a piezoelectric layer; an interdigital transducerelectrode over the piezoelectric layer, the interdigital transducerelectrode including a bus bar and a plurality of fingers extending fromthe bus bar, the plurality of fingers each including an edge portion anda body portion; a temperature compensation layer over the interdigitaltransducer electrode; and a mass loading strip overlapping the edgeportions of the plurality of fingers, the mass loading strip having adensity that is higher than a density of the temperature compensationlayer, the mass loading strip including a first layer and a secondlayer, a portion of the temperature compensation layer being positionedbetween the mass loading strip and the piezoelectric layer, the massloading strip arranged to suppress a transverse mode, and wherein themass loading strip includes a third layer.
 14. An acoustic wave filtercomprising: an acoustic wave resonator including a piezoelectric layer,an interdigital transducer electrode over the piezoelectric layer, atemperature compensation layer over the interdigital transducerelectrode, and a multi-layer mass loading strip overlapping edgeportions of fingers of the interdigital transducer electrode, themulti-layer mass loading strip having a higher density than thetemperature compensation layer, the multi-layer mass loading stripincluding a first layer and a second layer, the first layer positionedcloser to the interdigital transducer electrode than the second layer,and the first layer having a higher adhesion to the temperaturecompensation layer than the second layer; and a plurality of otheracoustic wave resonators coupled to the acoustic wave resonator, theacoustic wave resonator and the other acoustic wave resonators togetherarranged to filter a radio frequency signal.
 15. The acoustic wavefilter of claim 14 wherein the multi-layer mass loading strip is amulti-layer conductive strip.
 16. A method of filtering a radiofrequency signal, the method comprising: receiving a radio frequencysignal at an input port of an acoustic wave filter that includes anacoustic wave resonator, the acoustic wave resonator including amulti-layer mass loading strip overlapping edge portions of fingers ofan interdigital transducer electrode, a first layer of the multi-layermass loading strip having a higher adhesion to a temperaturecompensation layer than a second layer of the multi-layer mass loadingstrip, at least a portion of the temperature compensation layerpositioned between the multi-layer mass loading strip and theinterdigital transducer electrode, and the second layer of themulti-layer mass loading strip having a higher mass than the first layerof the multi-layer mass loading strip; and filtering the radio frequencysignal with the acoustic wave filter, the filtering includingsuppressing a transverse mode using the multi-layer mass loading stripof the acoustic wave resonator.
 17. The method of claim 16 wherein themulti-layer mass loading strip includes a titanium layer.
 18. The methodof claim 16 wherein the multi-layer mass loading strip is embedded inthe temperature compensation layer.
 19. The method of claim 16 whereinthe second layer of the mass loading strip has a mass sufficient tosuppress the transverse mode.
 20. The method of claim 16 wherein themulti-layer mass loading strip is spaced apart from a piezoelectriclayer of the acoustic wave resonator by a distance that is within 20% to80% of a thickness of the temperature compensation layer.